Page 37 - January 2009

the very distinguished Dr. Newton, whose praises I have already celebrated, and he in the month of October, 1706 was good enough to report to me what he and also what his friends have observed respecting this matter.
He recites that on a journey from Bologna towards Florence he heard at the city of San Michele in Bosco, near Bologna the sound of the firing of Cannon. These cannon were forty miles off, being fired at Mirandula, which a French army then held in siege. And on the following night he heard the same sound while he was resting over night in the Apennines, (twenty miles further off.)
But the observations and experiments which the same very eminent man through his politeness and benevolence caused to be made by others, justly claim for themselves a particular specification as well as my best thanks for these honors which his excellency has conferred upon me. When he received my letter at Florence he disclosed what I wanted to a certain nobleman who was at the same time an eminent philosopher; and he in turn communicated these wishes of mine to the Grand Duke. “The Grand Duke, as he says, in accordance with his singular love of the arts and of learned pursuits, as also in accordance with that gracious indulgence towards the votaries which he has received by inheritance from his ancestors along with his scepter, immediately gave orders that experiments should be made for the sake of fully satisfying me on this point; and he set Joseph Averrani a renowned philosopher of Pisa, and a man skilled in every one of the more liberal arts, over the inspection and direction of these experiments. The memoirs of this most honorable gen- tleman our most honorable envoy has deigned to write out at length for me. But the gist of the matter amounts to this: After having premised with equal caution and ingenuity very many things which might produce a great difference in the progress of sounds he at length proceeds as follows:
“In the lower fortress of Florence a culverin [a long-bar- reled cannon] was fired frequently between the first and the third hour of the night. Certain men at the same time were kept at Leghorn and were ordered diligently to observe whether they could hear its report. Of these men, some who had been stationed at the Lanterna and at Mazzoco heard no sound; (perhaps because the roar of the sea obscured the sound); but others who were standing on the bastions of the old fortress (which they call Donjon) and those who had been sent to Mount Rotondo (which is about five miles from Leghorn in the direction of Mount Nero) caught up the sound in their ears. And as often as the gun was fired its report was clearly heard in the same places. Now the distance of this Fortress of Florence from Mount Rotondo in a straight line is reckoned at not less than fifty five miles. And it is wor- thy of note that the intervening country was studded with many hills, which must needs have somewhat obstructed the path of the sound. To these considerations should be added that on the same evening a west wind was gently blowing which, (since Leghorn is situated to the south southwest with respect to Florence) may justly be supposed to have slightly impeded a freer expansion of the sound. In order however that an open place and one lying level in all directions might be obtained, that tract of the sea was selected which lies
between Leghorn and Port Ferraio, the distance of which, according to the calculation of the most skillful sailors, is set down, at sixty miles. The report, however, of artillery not infrequently reaches from Leghorn to this Port, and the places in its vicinage. Nor is there need of favoring winds to promote this passage of sound, in order that it may be surely heard. Indeed any wind whatsoever, whether it be favorable or adverse, is equally an impediment, and renders the sound less audible; it may be because the roar of the sea, agitated by this cause, is more a disadvantage than the current of the air blowing in the same direction is an advantage.
“Hence it is that the sound is heard only when the wind is entirely still or is only murmuring very gently—when the air is serene and the sea tranquil. Nor then, indeed, is it heard indiscriminately from all points, but only from those which are a little more elevated, such as the two bulwarks which are called Stella and Falcona and the place called Mulini. Moreover it is required that the observer should be as atten- tive as possible, and should not be hindered and troubled by the voice or clamor of persons making a din around him. But then equally by day and by night he may hear the sound pro- vided the atmosphere be clear and still—the only difference being that the sound seems somewhat stronger and clearer in the night time, when no noises occur such as are often wont to disturb the ears by day.
“Moreover, it has been reported to us by most credible witnesses that many years ago when an insurrection was rag- ing at Messina and the city was closely besieged, the sound of the guns startled the ears of the inhabitants of Augusta and of Syracuse [about 80 miles over water].
“Likewise when the French were shaking Genoa with heavy siege guns it is certain that the sound of the cannon reached as far as Mount Nero which overhangs Leghorn [about 90 miles over water].
“From these observations I am inclined to believe that there is no difference in this regard between Italy and the northern regions.
“But as regards the other question—whether a wind blowing directly or adversely accelerates or retards sound—it is not in my power as yet to give a certain reply. For the experiments which I have instituted and by which I had hoped that the truth would be explored, do not suffice for settling the question. In fact during the summer time (when for the most part the winds by day blow from the sea and from the west, while when evening comes on they are gener- ally still), the most suitable occasions for frequently and cer- tainly testing the matter were wanting to me. I hope, howev- er, that towards the close of the year, after weather of anoth- er kind shall have supervened, I may obtain more favorable opportunities for instituting and testing experiments of this kind with greater success and frequency, as also with greater accuracy. But for the present it must suffice to report what happened to me on the 10th of August last past, when I was permitted to try the following experiments:
“A culverin of a certain kind [culverina quaedani] was placed on the curtain of the lower fortress of Florence, and was so planted there that its mouth pointed towards Artemino, which is the country palace of the Grand Duke of
36 Acoustics Today, January 2009